Look at creating `Config` directly from dictionaries.

**Is your feature request related to a problem? Please describe.**

It is odd that `Config` shouldn't be `update`'d since it is a `dict` subclass. Doing so would completely bypass the schema validation, so we probably need to redefine `Config.update` and `Config.__setitem__` probably needs to be got rid of! Or possibly there is a better base for this class that gives dict like behaviour? We could possibly make it something with dot style access, like a Dotmap.

No file or test is named. Start by locating Config and reading its schema-validation, update, and item-assignment behavior; first settle the intended dictionary-like API, then add tests showing validation is preserved and the chosen behavior is complete.

Written by the indexing model from the issue text.